Just an improvement to assembly of the XY plotter: In my kit it is impossible to put the bracket in page 18 and page 19 on the desired position. The nuts do not have enough space since the motion slide is very close already.
However, it is possible to simply turn the bracket by 180 degrees. This seems to work well (much better as in the orginal instruction) and does not have any impact on further construction of the plotter or its functionality.
Here are two pictures that show how I placed it.
Meanwhile I also added a laser engraver and it is still working perfectly. 
Regards,
Mike